Coincidences Between Beta- and Gamma-Rays in Manganese

With two reliable high speed counters in a coincidence circuit of resolving time, τ=3.4×10^-7 min., coincidences have been recorded between beta- and gamma-radiation from Mn⁵⁶ (148 min.) formed by slow neutron capture. By interposing various thicknesses of aluminum between the source and the beta-ray counter, the ratio of beta-gamma coincidences to single beta-counts was observed as a function of the energy of the beta-rays. The number of coincidences per beta-ray was larger when electrons of all energies were striking the beta-ray counter than when only electrons of high energy were recorded. Coincidences were still recorded when only the high energy beta-rays were entering the counter. In addition gamma-gamma coincidences were found. From these experiments it is concluded that Fe⁵⁶ is formed in two excited states from the disintegration of Mn⁵⁶ and that one gamma-ray per disintegration is associated with the high energy group and about two gamma-rays per disintegration with the low energy group.